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Effect of filler metals on solidification cracking susceptibility of Al alloys 2024 and 6061
Accepted Manuscript Title: Effect of Filler Metals on Solidification Cracking Susceptibility of Al Alloys 2024 and 6061 Authors: Tayfun Soysal, Sindo Kou PII: DOI: Reference:
S0924-0136(18)30511-9 https://doi.org/10.1016/j.jmatprotec.2018.11.022 PROTEC 16015
To appear in:
Journal of Materials Processing Technology
Received date: Revised date: Accepted date:
27 August 2018 16 November 2018 17 November 2018
Please cite this article as: Soysal T, Kou S, Effect of Filler Metals on Solidification Cracking Susceptibility of Al Alloys 2024 and 6061, Journal of Materials Processing Tech. (2018), https://doi.org/10.1016/j.jmatprotec.2018.11.022 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Effect of Filler Metals on Solidification Cracking Susceptibility of Al Alloys 2024 and 6061
*Corresponding author. Email addresses: tsoys
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Tayfun Soysala and Sindo Koub* a Graduate Student, b Faculty of Materials Science and Engineering, the University of Wisconsin, Madison, WI 53706, United States
[email protected] (T. Soysal), [email protected] (S. Kou)
Graphic Abstract The effectiveness of filler metals in reducing the susceptibility of Al alloys
2024 and 6061 to solidification cracking was evaluated using the Transverse Motion Weldability
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(TMW) test, in which the lower sheet in lap welding is moved at the speed V in the transverse
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direction of welding to cause cracking in the weld. The speed V at which one weld edge moves
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away from the other during crack propagation is close to that in actual welding, thus suggesting
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the test results are realistic. For welding 2024 Al, filler metal 2319 Al was least effective and
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filler metals 4043 Al and 4145 Al were both very effective, especially 4145 Al. For welding
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6061 Al, the new commercial filler metal 4349 Al designed to increase the weld strength was as effective as filler metal 4043 Al, which has been widely used for reducing solidification cracking
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in 6000-series Al alloys.
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Abstract The effectiveness of filler metals in reducing solidification cracking in welds of 2024 Al and 6061 Al was examined, these two Al alloys being highly susceptible to solidification cracking. The effectiveness was evaluated by the transverse motion weldability (TMW) test.
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2024 Al was welded with filler metals 2319 Al, 4043 Al and 4145 Al. 4043 Al and 4145 Al both reduced cracking effectively, but 4145 Al was significantly better. 6061 Al was welded with filler metals 4043 Al and 4943 Al (a new alloy designed to increase the weld strength of the 6000-series alloys), and the effectiveness was similar. Micrographs and curves of temperature T vs. fraction solid fS of the weld metals were used to help explain the test results.
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Keywords: Welding, solidification cracking, aluminum alloys, filler metals, weldability test.
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1. Introduction
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Welds of aluminum (Al) alloys are known to be susceptible to cracking during solidification.
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Because of solidification shrinkage (solid density > liquid density) and thermal contraction, the
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mushy zone (a weak semisolid between the weld pool and the solidified weld metal) must shrink.
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However, the mushy zone cannot shrink freely because it is connected to the much bigger and more rigid workpiece. Shrinkage can be more difficult if the workpiece is clamped down tightly.
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This obstructed shrinkage induces tensile deformation in the transverse direction of the mushy zone to cause cracking. To reduce the crack susceptibility, filler metals with nonmatching
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compositions are often required to adjust the composition of the weld metal in the fusion zone.
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Friction-stir welding can produce good-quality Al welds. However, arc welding can still be more versatile and cost effective in many applications if effective measures can be taken against the formation of defects in welds, especially cracking during solidification. Dudas and Collins (1966) studied the susceptibility of high strength wrought Al alloys to solidification cracking in welding with matching and non-matching filler metals. 2024 Al was 2
reported as the most crack-susceptible alloy in the 2000-series (Al-Cu) alloys, and 6061 Al the most crack-susceptible of all the Al alloys tested (Dudas and Collins, 1966). The filler metal 4043 Al significantly reduced crack susceptibility of 6061 Al, but no filler metal was reported to
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reduce the crack susceptibility of 2024 Al (Dudas and Collins, 1966). Many solidification cracking tests have been developed to evaluate the crack susceptibility of alloys. So far, the solidification cracking test most widely used in the welding industry and research has been the Varestraint test developed by Savage and Lundin (1965). The standard workpiece is 203 mm long by 102 mm wide by 12.7 mm thick. During welding, the workpiece of
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thickness H is suddenly bent in the welding direction against a mandrel (bending block) of
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predetermined radius R. A tensile strain of = H/(2R+H) × 100 % is induced at the top surface
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of the workpiece. The strain induces tension in the mushy zone to cause solidification cracking.
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The total or maximum crack length is used as the index for the susceptibility to solidification
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cracking. A transverse version of the Varestraint test, called transverse Varestraint, was
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subsequently developed by Senda et al. (1971, 1973), in which the workpiece is bent suddenly in the transverse direction of welding instead of longitudinal.
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Coniglio (2008) pointed out that the tensile strain in the Varestraint test is the global strain
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in the workpiece, instead of the local tensile strain in the mushy zone responsible for solidification cracking. He also pointed out that the strain rate caused by sudden bending is too
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fast as compared to that in welding practice. Another issue is associated with evaluating the effect of a filler metal on solidification cracking. The filler metal increases H by forming a crown on the workpiece surface. The crown height varies across the width of the weld, so does H and hence . This issue may be ignored if only a qualitative comparison of weldability is needed, without specifying the strain level of the weld. To avoid this issue, however, a two-step 3
procedure is needed, an example of which was described by Lippold et al. (1982). The first step is to make a bead-on-plate weld with a filler metal, and then remove the crown by milling to ensure a flat workpiece surface. The second step is to conduct the normal Varestraint test (gas-
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tungsten arc welding without a filler metal) by making a smaller weld within the fusion boundary of the first weld.
To help address these and other issues (such as the interference of solidification by liquation cracking) associated with Varestraint testing (Savage and Lundin, 1965; Senda et al., 1971, 1973), Soysal and Kou (2017, 2018) developed a simple test, called Transverse-Motion
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Weldability (TMW) test, in which lap welding is conducted while the lower sheet moves normal
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to the welding direction at a predetermined speed to induce transverse tension in the mushy zone
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and cause solidification cracking. As the lower sheet moves at the speed V, the weld edge on it
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also moves away at V from the stationary weld edge on the upper sheet. In the TMW test V can
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be as slow as that in actual gas-tungsten arc welding, in which one weld edge also moves away
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from the opposite weld edge spontaneously as shown by Matsuda et. al. (1980). The test can be conducted with or without a filler metal for welding. Filler metals were used and the test results
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(Soysal and Kou, 2017) were consistent with the filler metal guides (AlcoTec Wire Co.; Hobart Filler Met.). The test was also conducted without filler metals (Soysal and Kou, 2018). The crack
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susceptibility ranking was 6061 Al > 7075 Al > 2024 Al > 2219 Al, which agrees with the crack
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susceptibility ranking of commercial wrought Al alloys. Before the TMW test the Controlled Tensile Weldability (CTW) test was developed by
Coniglio et al. (2009). In the CTW test the workpiece is welded to a larger and thicker mounting plate, one on each lateral side. The plates were then mounted on a horizontal tensile testing machine to stretch the workpiece to induce tension in the transverse direction of the weld. Since 4
the mounting plates, workpiece, solidified weld metal and semisolid mushy zone are all being deformed during welding, an extensometer is mounted across the weld width on the bottom surface of the workpiece to measure the speed at which one weld edge moves away from the
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opposite weld edge, i.e., transverse deformation rate of the mushy zone. The test Soysal and Kou (2017, 2018) developed has some similarity to the CTW test, but the mounting plates, extensometer and tensile testing machine are not required.
The present study evaluated effectiveness of filler metals in reducing solidification cracking in two highly crack susceptible Al alloys, 2024 and 6061. The purpose was to provide
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experimental data that can be used for selecting filler metals to suppress solidification cracking
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in welding 2024 Al and 6061 Al.
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2. Experimental Procedure
The transverse-motion weldability (TMW) test used for assessing the solidification cracking
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susceptibility has been described in detail elsewhere (Soysal and Kou, 2017, 2018) and will not
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be repeated here. As shown in Fig. 1, during lap welding the upper sheet is stationary and the lower sheet moves at a predetermined speed V normal to the welding direction to induce tensile
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deformation in the mushy zone to cause cracking.
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Table 1 shows the actual compositions of the workpiece and filler metals (1.2 mm diameter)
used for welding. The upper sheet was 3.2 mm by 51 mm by 203 mm, and the lower sheet 3.2
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mm by 127 mm by 152 mm. The lower sheet was positioned to stick out of the upper sheet by 19 mm (0.75 in) before welding. A servomotor was preprogrammed by a computer to move the lower sheet. Apparently, by moving the lower sheet at a single constant speed throughout welding, the crack susceptibility can be evaluated based on crack initiation. However, in gas-
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metal arc welding the filler metal tends to freeze faster and melt the workpiece less at the beginning of welding than during the steady state because the workpiece is initially cold. This can cause considerable scatter in the test results. Thus, it was decided to move the lower sheet
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faster initially to insure crack initiation and then slower for crack propagation. Consequently, in all experiments the moving speed of the lower sheet was 1.5 mm/s initially for a distance up to about 25 mm and then lowered to the predetermined level to investigate crack propagation. After the lower sheet started to move, the carriage was turned on to move the torch at the
Mushy-zone deformation rate = V
GMAW torch
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torn weld low er sh ee t
up (st p e r ati sh on ee ary t ) we dir ldin ec g tio n
low (m er s ov hee ing t )
arc pool
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screw
mushy zone moving at speed V
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predetermined travel speed, and the arc was initiated.
V
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crack
guide sheet
Cu base
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Fig. 1. Schematic sketch of test used for assessing susceptibility to solidification cracking (Soysal and Kou, 2017).
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The welding conditions for gas-metal arc welding (GMAW) were: 23 V welding voltage, 5.1
mm/s torch travel speed, 85 - 89 mm/s wire feed speed (welding current of 120 - 125 A), and
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3.54 x 10-4 m3/s Ar shielding. The torch was tilted 10o toward the joint and 10o backward (dragging). After welding, the fracture surfaces were examined by scanning electron microscopy (SEM). The transverse cross-sections of the welds were cut and mechanically polished. 6061 Al welds 6
were etched with Keller’s solution, consisting of 5 mL HNO3, 3 mL HCl, 2 mL HF and 190 mL distilled water. 2024 Al welds were etched with a solution consisting of 0.5 mL HF and 99.5 mL distilled water. The welds were then examined under optical and electron microscopy.
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3. Results Fig. 2 shows a 2024 Al workpiece after being welded with filler metal 2319 Al. The weld surface was cleaned with a stainless-steel wire brush before photographing. The initial moving speed of the lower sheet was 1.5 mm/s, resulting in the initial portion of the weld with a wider crack opening. After lowering the moving speed to 0.2 mm/s, the crack opening narrowed. The
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length of the narrower crack is labeled as Lcrack, and the length of the weld without the wider
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opening is labeled as Lweld. The ratio of Lcrack/Lweld is taken as the normalized length of crack
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propagation. The welds in the present study are shorter than those gas-metal arc welds in the
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previous study by the authors (Soysal and Kou, 2017). It was found that the results of shorter
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welds are more reproducible, i.e., with a narrower transition range from no crack to full crack. A
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longer weld tends to get wider as it approaches the end of the workpiece. The dendritic fracture surface shown by the SEM image in Fig. 3 confirms that the crack was caused by solidification
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cracking. The fracture surfaces of cracks that occur during solidification in welding and casting typically reveal dendrites (Matsuda et al.1978; Campbell, 2003). This is because such cracking
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occurs along grain boundaries near the end of solidification, along which thin liquid films are
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present. When cracking occurs, the thin liquid films quickly freezes over the dendrite arms, thus resulting in dendritic fracture surfaces. 3.1 Assessing filler-metal effectiveness Fig. 4 shows the welds made by welding 2024 Al with three different filler wires at the lowersheet moving speed of 0.4 mm/s. When filler wire 2319 Al is used, solidification cracking 7
propagates all the way through the weld. When the filler wire is switched to 4043 Al, solidification cracking is greatly reduced, propagating only slightly after the initiation period. With 4145 Al, the reduction is even better – no crack propagation at all. The results show clearly
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that filler metal 4043 Al or 4145 Al can be considered if solidification cracking occurs in welding 2024 Al.
In Fig. 5 the normalized crack length is plotted vs. the lower-sheet moving speed V for the 2024 Al welds made with the three filler wires. As shown in Fig. 5a, with filler metal 2319 Al the normalized crack length increases from 0 at V = 0.1 mm/s to 1.0 at 0.3 mm/s. The range of V
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over which the normalized crack length increases from 0 to 1.0 will be called the transition range
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2319 Al under the welding conditions used.
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hereinafter. Thus, the transition range is 0.10 – 0.30 mm/s for 2024 Al welded with filler metal
Fig. 2. 2024 Al welded with filler metal 2319 Al: (a) overview, (b) enlarged. Lower sheet initially moved at 1.5 mm/s to ensure crack initiation and lowered to 0.2 mm/s for crack 8
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propagation. Lcrack and Lweld are, respectively, length of crack propagation and length of weld from beginning of crack propagation.
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Fig. 3. Dendritic fracture surface of 2024 Al weld made with filler metal 2319 Al confirming solidification cracking.
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Fig. 4. 2024 Al welded with filler metals: (a) 2319 Al, (b) 4043 Al, and (c) 4145 Al and tested with the moving speed of 0.4 mm/s.
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Similar results are shown in Fig. 5b for 2024 Al welded with filler metal 4043 Al and in Fig.
5c for 2024 Al welded with filler metal 4145 Al. As shown, the transition range increases to 0.36 – 0.50 mm/s with filler metal 4043 Al. It increases further to 0.88 – 1.0 mm/s with filler metal 4145 Al.
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Fig. 6 shows the results of 6061 Al welded with two different filler metals. As shown in Fig. 6a, with filler metal 4943 Al the transition range is from 0.40 to 0.50 mm/s. With 4043 Al as the filler metal, the transition range is from about 0.38 to 0.50 mm/s as shown in Fig. 6b.
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Fig. 7 summarizes the results of the assessment of filler-metal effectiveness. A transition range at a higher V level suggests the lower sheet needs to be moved faster to cause cracking and hence a more effective filler metal for reducing cracking. As shown, filler metal 2319 Al is least effective for 2024 Al, and filler metal 4145 Al most effective. Filler metals 4943 Al and 4043 Al have similar effectiveness. Filler metal 4043 Al appears to reduce the crack susceptibility of
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2024 Al and 6061 Al to about the same level.
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2024 Al welded with three filler metals
1.0 0.9 0.8 0.7 0.6
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1.0
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Filler: 4145 Al
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full crack
0.2 0.4 0.6 0.8 Moving speed V, mm/s
transition range
0.2 0.4 0.6 0.8 Moving speed V, mm/s
full crack
0.5 0.4 0.3 0.2 0.1 0 0
transition range
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1.0 0.9 0.8 0.7 0.6
1.0
Filler: 4043 Al
no crack
0.5 0.4 0.3 0.2 0.1 0 0
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full crack
no crack
0.2 0.4 0.6 0.8 Moving speed V, mm/s
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Normalized crack length, Lcrack / Lweld
(c)
transition range
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Normalized crack length, Lcrack / Lweld
(b)
0.5 0.4 0.3 0.2 0.1 0 0
Filler: 2319 Al
no crack
Normalized crack length, Lcrack / Lweld
(a) 1.0 0.9 0.8 0.7 0.6
1.0
Fig. 5. Test results of 2024 Al welded with three filler metals: (a) 2319 Al; (b) 4043 Al; (c) 4145 Al.
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6061 Al welded with two filler metals
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full crack 1.0
Filler: 4043 Al
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transition range
0.2 0.4 0.6 0.8 Moving speed V, mm/s
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0.5 0.4 0.3 0.2 0.1 0 0
0.2 0.4 0.6 0.8 Moving speed V, mm/s
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1.0 0.9 0.8 0.7 0.6
transition range
no crack
0.5 0.4 0.3 0.2 0.1 0 0
Filler: 4943 Al
full crack
Normalized crack length, Lcrack / Lweld
(b)
1.0 0.9 0.8 0.7 0.6
no crack
Normalized crack length, Lcrack / Lweld
(a)
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Fig. 6. Test results of 6061 Al welded with two filler metals: (a) 4943 Al; (b) 4043 Al. (b) 6061 Al welded with filler metals 4043 Al, 4943 Al 1.0 full 0.8 crack
0.6
full crack
Moving speed V, mm/s
0.8
transition range
1.0
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2024 Al welded with filler metals 2319 Al, 4043 Al, 4145 Al
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Moving speed V, mm/s
(a)
0.4
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0.2 0
2319
no crack 4043
4145
increasing filler-metal effectiveness in reducing crack susceptibility (faster V required to cause cracking)
0.6 0.4 no crack
0.2 0
4043
4943
similar effectiveness
Fig. 7. Results of assessment of filler-metal effectiveness in welding: (a) 2024 Al (Fig. 5); (b) 6061 Al (Fig. 6). The faster the lower-sheet moving speed is required to stretch the mushy zone to cause cracking, the more effective the filler metal is in reducing the crack susceptibility.
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3.2 Macrostructure and microstructure Fig. 8 shows the transverse cross-section of a 2024 Al weld made with filler metal 4145 Al. The areas of the upper and lower sheets in the weld represent the contribution of the base metal
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to the weld metal. The dilution level, i.e., the extent the filler metal is diluted by the base metal, is the ratio of the areas to the total area of the weld. It is about 50% for the 2024 Al welds and 47% for the 6061 Al welds. For each weld, the weld-metal composition can be calculated from the compositions of the workpiece and filler wire and the dilution level (Kou, 2003). The small rectangular box indicates the location where micrographs in Figs. 9 and 10 are shown in this and
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the other welds, that is, the mid height of the fusion boundary in the upper sheet. Near the fusion
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zone the heat-affected zone appears as a lighter-etching region due to solutionization of the
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precipitates present in the original workpiece. Farther away from the fusion zone, it appears as a
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darker-etching region of the precipitates that formed due to heating during welding (Kou, 2003).
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Fig. 8. Transverse cross-section of 2024 Al weld made with filler metal 4145 Al. Small rectangular box indicates location where micrographs were taken, i.e., fusion boundary at mid height of upper sheet. Solid lines indicate the fusion boundaries, and dotted lines the surfaces of the upper and lower sheets before welding. Fig. 9 shows the microstructure near the fusion boundaries of the 2024 Al welds made with
filler metals 2319 Al, 4043 Al and 4145 Al. The small boxes in Fig. 9b and c indicate the locations where the SEM images in Fig. 11 were taken. Dendritic columnar grains can be seen in the weld metal. The eutectic exists in the interdendritic areas. With much Si provided by fillers 13
4043 Al and 4145 Al, the eutectic becomes darker etching than without Si. Fig. 10 shows the microstructure near their fusion boundaries of the 6061 Al welds made with filler metals 4943 Al and 4043 Al. The eutectic appears very thin but still continuous. Fig. 11 shows the SEM images
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of the eutectics in 2024 Al welds made with filler metals 4043 Al and 4145 Al. The results of
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EDX composition measurements are given in Table 2. As shown, these eutectics are Si rich.
Fig. 9. Optical micrographs near fusion boundaries (dotted lines) of 2024 Al welded with fillers: (a) 2319 Al; (b) 4043 Al; (c) 4145 Al. Rectangular boxes in (b) and (c) indicate the locations where SEM images in Fig. 11 were taken. 14
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Fig. 10. Optical micrographs near fusion boundaries (dotted lines) of 6061 Al welded with fillers: (a) 4943 Al; (b) 4043 Al. Very thin but still continuous eutectic (dark etching) suggests thin continuous liquid films near end of solidification.
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3.3 T-fS Curves for 2024 Al welds made with filler metals 4043 and 4145 Al
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As mentioned previously, the level of filler-metal dilution by the base metal can be
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determined from the transverse macrograph of the weld. The dilution level can in turn be used to calculate the weld-metal composition (Kou, 2003) as follows: (wt% of element E in weld metal)
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= (wt% of element E in base metal) × (dilution) + (wt% of element E in filler metal) × (1 − dilution). Table 3 shows the compositions of the 2024 Al welds made with filler metals 4043 and
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4145 Al. Based on these compositions, the commercial thermodynamic software Pandat (2018), the aluminum database PanAluminum (2018) and the Scheil solidification model were used to calculate the curves of T (temperature) vs. fS (fraction solid) of these welds. These curves, i.e., the solidification paths, of the welds are shown in Fig. 12. The points at which solid phases begin
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to form during solidification are indicated. As can be seen on both curves, the FCC phase (the Al-rich phase) starts to form first and other phases follow. The diamond phase is essentially pure Si with the trace amount of Al in it. Fig. 12a shows Al3Ti precipitates from the liquid (at 669 oC)
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before the FCC phase starts to form. As shown in Table 1, filler metal 4043 Al contained 0.2 wt%
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Ti.
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Fig. 11. SEM images of eutectics in 2024 Al welded with fillers: (a) 4043 Al (inside boxed area in Fig. 9b); (b) 4145 Al (inside boxed area in Fig. 9c). The compositions measured by EDX at the locations indicated by the circles are given in Table 2.
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The phases shown along the T-fs curves in Fig. 12 can be compared with the results of EDX
measurements in Table 2 to help identify the phases shown in Fig. 11. For 2024 Al welded with filler metal 4043 Al (Fig. 11a), in view of the Si and Al contents, Point 1 in Fig. 11a seems to correspond to the combination of the FCC phase and the diamond phase. Likewise, in view of
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the Si, Cu and Al contents, Point 2 seems to correspond to FCC + diamond + AlCu_Ө. As for 2024 Al welded with filler metal 4145 Al (Fig. 11b), Point 1 seems to correspond to FCC + diamond phases. Point 2 is likely to correspond to the combination of FCC + diamond +
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β_AlFeSi + Al15_FeMn3Si2 + AlCu_Ө.
Solidification paths of 2024 Al welds 650
Al3Ti
made with filler 4043 Al
Al15_FeMn3Si2
Fcc
β_AlFeSi
600
Diamond (Si) 550 AlCu_Ө 0.2
0.4 0.6 fraction solid fs
650
made with filler 4145 Al Fcc
Al15_FeMn3Si2
600
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Diamond (Si) β_AlFeSi
550
Q_Al5Cu2Mg8Si6 0
0.2
AlCu_Ө
0.4 0.6 fraction solid fs
1
0.8
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500
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Temperature T, ºC
(b)
1
0.8
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0
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500
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Al8FeMg3Si6+Q_Al5Cu2Mg8Si6
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Temperature T, ºC
(a)
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Fig. 12. Solidification paths calculated using Pandat and PanAluminum for 2024 Al welds made with fillers: (a) 4043 Al; (b) 4145 Al. Discussion
4.1
Crack initiation and propagation
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4.
As mentioned previously, at the beginning of GMAW filler-metal droplets tend to freeze
faster and hence less able to melt the base metal because the workpiece is still cold. This can cause scatter in the results of crack-susceptibility testing based on crack initiation, i.e., moving the lower sheet at a constant speed V throughout welding. To avoid this problem, crack 17
susceptibility testing was conducted based on crack propagation, i.e., moving the lower sheet faster initially to ensure crack initiation but slower subsequently for crack propagation. Crack susceptibility testing based on crack propagation instead of crack initiation can be
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justified as follows. Kou (2015) proposed a criterion for cracking during solidification by considering the space between two columnar dendritic grains near their roots. He showed that for a weld metal with a higher maximum │dT/d(fS)1/2│ (T: temperature; fS: fraction of solid), the space decrease caused by its slower grain growth and liquid feeding is more likely to be slower than the space increase caused by the tensile deformation separating the grains (Kou, 2015).
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Thus, it is more likely for a void (i.e., crack) to form inside the space either by nucleation (crack
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initiation) or by extension of an existing crack into it (crack propagation). Consequently, a weld
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metal with a higher maximum │dT/d(fS)1/2│ can rank higher in the crack susceptibility in the
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present test either based on crack initiation or crack propagation. Oxides or micro porosity can
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serve as the sites for nucleation of cracks (Campbell 2003; Coniglio, Cross, 2009), so can the
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free surface of the mushy zone (Campbell, 2014). In lap welding such as the present test, the free surface includes the surface of the mushy zone at the top and that on the side at the gap between
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the upper and lower sheets. Soysal and Kou (2017, 2018) demonstrated that the cracksusceptibility ranking of commercial wrought Al alloys using the present test based on crack
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propagation agrees with the ranking predicted based on the maximum│dT/d(fS)1/2│as the crack
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susceptibility index. Furthermore, it also agrees with the ranking reported by Dowd (1952) and Dudas and Collins (1966) using other crack-susceptibility tests. The crack susceptibility of the welds in the present study was also predicted based on the maximum│dT/d(fS)1/2│and the weldmetal compositions, and it agreed well with the test results (Soysal and Kou, 2018b).
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Kou’s criterion for solidification cracking and index for the crack susceptibility (Kou, 2015) can be related to the TMW test. In the TMW test the motion of lower sheet during lap welding
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can cause the columnar grains near the centerline of the mushy zone to separate from each other. For an alloy with a high │dT/d(fS)1/2│near (fS)1/2=1, the grains grow thicker slowly near their roots as they grow longer to form a long liquid channel between them to resist liquid feeding, thus delaying the bonding between the grains and slowing down liquid feeding through the channel. Consequently, even a slow speed of the lower sheet can separate the grains to cause
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cracking before bonding or liquid feeding can occur to resist cracking. The slower the speed is,
Effectiveness of filler metals
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4.2
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the higher the crack susceptibility.
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Al filler metal guides (AlcoTec Wire Co.; Hobart Filler Met.) provide useful information for
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designing the welds for various purposes or applications of Al welds, such as better resistance to
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solidification cracking, higher strength, better resistance to corrosion etc. However, they do not include 2024 Al. Fig. 7a can be a guide for selecting filler metals to minimize the chance for
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solidification cracking to occur in welding 2024 Al.
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By keeping the welding parameters the same in making welds with different filler metals, the effect of the filler metal on solidification cracking can be evaluated. When the filler metal is
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changed, the composition, solidification path and hence crack susceptibility of the weld metal are changed significantly. The weld width may also be changed, but usually not much. Ideally, the welding parameters can be changed slightly to keep the weld width identical, but this is very difficult to do, and the effect may be small. The welding parameters can affect solidification cracking, but the effect of the weld-metal composition dominates (Kou, 2003). This is why an 19
alloy that has a high tendency to crack in casting also has a high tendency to crack in welding. If changing the welding parameters increases the dilution, the effectiveness of the filler metal in reducing cracking can be expected to decrease. In MIG welding, increasing the welding current
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(the wire feeding speed) causes more base metal to melt but more filler metal also melts. So, the dilution may not change a lot. Decreasing the travel speed can have a similar effect on dilution. Fig. 7a shows the transition range above which the lower sheet needs to be moved to cause full cracking in welds of 2024 Al and hence the effectiveness of the filler metal in reducing their solidification cracking are affected significantly by the filler metal used. 4145 Al is most
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effective and 2319 Al least.
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The filler metal guide (Hobart Filler Met.) indicates the new filler metal 4943 Al is effective
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for reducing solidification cracking in 6000 series Al alloys, without referring to the dilution level or any reports of crack susceptibility testing. As can be seen in Table 1, 4943 Al is close to
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4043 Al in composition, but the Mg/Si ratio is raised significantly to 0.074 in 4943 Al from
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0.010 in 4043 Al to increase the weld-metal strength. According to the developer of 4943 Al, the weld made with 4943 Al is higher in strength than that made with 4043 Al in the as-welded
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condition and is heat-treatable to gain extra strength by postweld artificial aging (Maxal).
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However, it is unclear how this much higher Mg/Si ratio may affect solidification cracking. The test results shown in Fig. 7b indicate that the effectiveness of 4943 Al in reducing solidification
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cracking in welding 6061 Al is similar to that of 4043 Al, at least under the experimental condition used in the present study. Fig. 9 shows a dark-etching phase appears in the fusion-zone microstructure of 2024 Al (~Al-4.6Cu) when the filler metal is changed from 2319 Al (~Al-6.3Cu) to 4043 Al (~Al-5Si).
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The calculated solidification paths of the 2024 Al welds made with filler metal 4043 Al and 4145 Al are shown in Fig. 12. With filler 4043 Al, the Si-rich phase (diamond A4 in structure) starts to form at about fS = 0.8 (about T = 550°C). With filler metal 4145 Al, the Si-rich phase starts to
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form significantly earlier at about fS = 0.6 (about T = 555°C). In both cases, the increase in the fraction solid with cooling is faster after (than before) the Si-rich phase starts to form. With 4145 Al, the fraction solid increases rapidly with decreasing temperature, causing the Al-rich dendrites to quickly bond together to resist solidification cracking (Kou 2015), (Liu and Kou, 2015, 2016, 2017), (Liu, Duarte and Kou, 2017). Although 4145 Al best resists solidification cracking in
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2024 Al, other weld properties need to be considered as well, e.g., toughness and corrosion
Strain rate in mushy zone
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4.3
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resistance, depending on the application of the resultant weld.
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In gas-tungsten arc welding of Al alloys, Matsuda et. al. (1980) measured the speed at which
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one weld edge moved away from the opposite weld edge, and it was in the range of 0-0.9 mm/s,
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close to that in Figs. 5 and 6. Thus, in the TMW test the speed V of the weld edge on the lower sheet relative to that on the upper sheet is realistic from the practical welding point of view, and
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the strain rate experienced by the mushy zone can be expected to represent that in actual welding.
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Although the average strain rate of the mushy zone in the transverse direction can be taken as V divided by the weld width W, the local strain rate near the crack is likely significantly higher than
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V/W. Bakir et al. (2018) measured the local strain rate near the crack in laser-beam welding of a stainless steel during the CTW test. At the crosshead speed of 1.2 to 2.3 mm/s of the tensile testing machine, the global strain rate of the entire mushy zone was 4 to 8 %/s and the local strain rate near the crack was 18 to 29 %/s.
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It might be possible to estimate the local strain rate near the crack in the TMW test. The transverse micrographs of the TMW tested welds showed no evidence of separation of dendrites from each other except near the crack (Soysal and Kou, 2018). In the areas next to both sides of
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the main crack, intergranular micro fissures were found, more or less parallel to the crack and often filled with dark-etching eutectic (not shown). Closer to the crack, the micro fissures were wider. Thus, as an approximation, tensile deformation can be assumed to occur mostly in the areas next to both sides of the main crack. Preliminary examination of transverse micrographs near cracks in some welds showed the total width of these areas was on the order of 1 to 2 mm.
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This suggests that, just before cracking occurred, the width of the area deformed by tensile
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deformation, D, was about 1.5 mm. The width of the weld and hence the mushy zone W was on
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the order of 10 mm. Thus, the local average strain rate V/D was significantly higher than the
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overall average strain rate V/W. If 2024 Al welded with filler metal 4043 Al is taken as an example just for the purpose of discussion, the minimum V needed to cause cracking is about 0.4
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mm/s according to Fig. 5b. The corresponding minimum overall average strain rate is V/W =
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0.04/s (0.4 mm/s ÷ 10 mm) or 4%/s. Likewise, the corresponding minimum local average strain
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rate is V/D = 0.27/s (0.4 mm/s ÷ 1.5 mm) or 27%/s. Further analysis of the local average strain rate is needed but not here as the focus of the present study is on the effectiveness of filler metals
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in reducing the crack susceptibility.
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4. Conclusions
The effect of the commercial Al filler metals on reducing the solidification-cracking
susceptibility of two highly crack susceptible Al alloys 2024 and 6061 was investigated using the TMW test. The following conclusions can be drawn from the test results:
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1. For welding 2024 Al, filler metal 4145 Al is highly effective against solidification cracking, 4043 Al less effective, and 2319 Al least effective. Thus, in situations where solidification cracking in 2024 Al welds is a major concern, 4043 Al or 4145 Al can be
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considered as the filler metal. 2. The calculated solidification paths of the 2024 Al welds show that the Si-rich phase tends to form at about 550 – 555oC during solidification but significantly earlier with filler metal 4145 Al than 4043 Al. With 4145 Al, after the formation of the Si-rich phase, the fraction solid increases rapidly during cooling to bond the Al-rich dendrites to resist
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cracking.
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3. For welding 6061 Al, the new filler metal 4943 Al is as effective against solidification
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cracking as the traditional filler metal 4043 Al. Thus, if a high weld-metal strength is a
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high priority, filler-metal 4943 Al can be considered.
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5. Acknowledgements
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This work was supported by the National Science Foundation under Grant No. DMR 1500367. The graduate student Tayfun Soysal was funded by the Ministry of National Education of
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Republic of Turkey during the project.
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6. References
AlcoTec Wire Corporation, 2015. www.alcotec.com/us/en/support/upload/ALC-
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10030C_AlcoTec_Alloy_Selection_Brochure_Tabloid.pdf.
Bakir, N., Gumenyuk, A., Rethmeier, M., 2018. Investigation of solidification cracking susceptibility during laser beam welding using an in-situ observation technique, Sci. Tech. Weld. Join., 23(3), 234–240.
23
Campbell J., Castings, 2nd edition, Butterworth Heinemann, Oxford, UK, 2003; pp. 216-247. Campbell, J., Private Communications, United Kingdom, June 2014. Coniglio, N., 2008. Aluminum alloy weldability: Identification of weld solidification cracking
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mechanisms through novel experimental technique and model development. Doctoral thesis, Otto-von-Guericke University, Magdeburg, Berlin.
Coniglio, N., Cross, C.E., 2009. Mechanisms for solidification crack initiation and growth in aluminum welding. Metal. Mater. Trans. A, 40A (11), 2718–2728.
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Cross, C. E., 2015. On the Origin of Weld Solidification Cracking, Hot Cracking Phenomena in
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Welds, 3-18.
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Dowd, J. D. 1952. Weld cracking of aluminum alloys. Weld. J., 31, 448s-456s.
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Dudas, J. H., and Collins, F. R. 1966. Preventing weld cracks in high strength aluminum alloys.
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Hobart Filler Metals, 2018.
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Weld. J., 45, 241s-249s.
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http://www.hobartbrothers.com/downloads/aluminum_selecti_1lOo.pdf Kou, S., 2015. A criterion for cracking during solidification. Acta Mater., 88, 366-374.
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Kou, S., Welding Metallurgy, 2nd edition, J. Wiley and Sons, Hoboken, NJ, 2003; pp. 103-114,
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149-151.
Liu, J., Kou S., 2015. Effect of diffusion on susceptibility to cracking during solidification, Acta Mater., 100, 359-368.
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Liu, J., Kou S., 2016. Crack susceptibility of binary aluminum alloys during solidification, Acta Mater., 110, 84-94. Liu, J., Kou, S., 2017. Susceptibility of ternary aluminum alloys to cracking during solidification,
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Acta Mater., 125, 513-523. Liu, J., Duarte H.P., Kou S., 2017. Evidence of back diffusion reducing cracking during solidification, Acta Mater., 122, 47-59.
Matsuda, F., Nakata, K., Harada, S., 1980. Moving characteristics of weld edges during
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solidification in relation to solidification cracking in GTA weld of aluminum alloy thin sheet
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(Weld. Mech., Strength & Design). Trans. JWRI, 9(2), 225-235.
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Matsuda, F., Nakagawa, H., Ogata, S., Katayma, S., 1978. Fractographic Investigation on
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Solidification Crack in the Varestraint Test of Fully Austenitic Stainless Steel-Studies of
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Fractography of Welded Zone (III). Trans. JWRI, 7(1), 59-70.
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Maxal, 2008. Maxal 4943. Maxal, Traverse City, MI, may be accessible at www.maxal.com/4943_datasheet.pdf,
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PanAluminium, 2018. Thermodynamic database for commercial aluminum alloys, Computherm
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LLC, Madison, WI 53719, 2018. Pandat, 2018. Phase diagram calculation software package for multicomponent systems,
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Computherm LLC, Madison, WI 53719, 2018.
Savage, W.F., Lundin, C.D., 1965. The Varestraint test, Weld. J. 44, 433s-442s.
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Senda, T., Matsuda, F., Takano, G., 1973. Solidification crack susceptibility for weld metals with the Trans-Varestraint test. Part 2: Commercially Used Aluminum and Aluminum Alloys. Yosetsu Gakkai- Shi. 42(1), 48-56.
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Senda, T., Matsuda, F., Takano, G., Watanabe, K., Kobayashi, T., Matsuzaka, T., 1971. Fundamental investigations on solidification crack susceptibility for weld metals with TransVarestraint test. Trans. Japan Weld. Soc., 2(2), 141-162.
Soysal, T., Kou, S., 2017. A simple test for solidification cracking susceptibility and filler metal
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effect. Weld. J., 96(10), 389s-401s.
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Soysal, T., Kou, S., 2018a. A simple test for assessing solidification cracking susceptibility and
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checking validity of susceptibility prediction. Acta Mater., 143, 181-197.
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Soysal, T., Kou, S., 2018b. Prediction of Filler-Metal Effect on Solidification Cracking in 2024
A
CC
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Al and 6061 Al, Sci. Tech. Weld. and Join., in preparation.
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Si
Fe
Cu
Mn
Mg
Cr
Ti
Zr
Zn
Al
0.01 0.01
0.01 -
-
Bal. Bal.
-
0.18 -
0.10 0.04 -
Bal. Bal. Bal. Bal.
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Sheets 2024 0.08 0.16 4.6 0.61 1.3 0.01 0.02 6061 0.666 0.387 0.245 0.099 1.083 0.1 0.025 Wires 2319 0.1 0.15 6.3 0.3 0.15 4043 5.2 0.8 0.3 0.05 0.05 0.001 0.20 4145 9.9 0.2 3.9 0.01 0.05 0.01 4943 5.42 0.12 0.005 0.005 0.4 0.001 0.017 Table 1. Actual compositions of materials in weight percent.
V
Si Fe Cu Mn Mg Al wt%; at% wt%; at% wt%; at% wt%; at% wt%; at% wt%; at% 2024-4043 Pt 1 13.6; 13.1 86.4; 86.9 2024-4043 Pt 2 9.7; 10.9 23.7; 11.7 66.6; 77.4 2024-4145 Pt 1 36.5; 35.5 0.6; 0.7 62.9; 63.8 2024-4145 Pt 2 12.5; 15.3 6.6; 4.1 27; 14.7 4.6; 2.9 49.3; 63.0 Table 2. Compositions (in weight % and atomic %) measured by EDX in 2024 Al welds made with filler metals 4043 and 4145 Al.
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A
N
U
Base-Filler #
A
CC
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Si Fe Cu Mn Mg Cr Ti V Zr Zn Al sheet-filler dilution 2024-4043 48.7 % 2.71 0.49 2.39 0.32 0.66 0.01 0.11 0.00 0.00 0.05 Bal 2024-4145 50.7 % 4.92 0.18 4.25 0.31 0.68 0.01 0.01 0.01 0.01 002 Bal Table 3. Compositions (in weight %) of 2024 Al welds made with filler metals 4043 and 4145 Al.
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S0924-0136(18)30511-9 https://doi.org/10.1016/j.jmatprotec.2018.11.022 PROTEC 16015
To appear in:
Journal of Materials Processing Technology
Received date: Revised date: Accepted date:
27 August 2018 16 November 2018 17 November 2018
Please cite this article as: Soysal T, Kou S, Effect of Filler Metals on Solidification Cracking Susceptibility of Al Alloys 2024 and 6061, Journal of Materials Processing Tech. (2018), https://doi.org/10.1016/j.jmatprotec.2018.11.022 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Effect of Filler Metals on Solidification Cracking Susceptibility of Al Alloys 2024 and 6061
*Corresponding author. Email addresses: tsoys
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Tayfun Soysala and Sindo Koub* a Graduate Student, b Faculty of Materials Science and Engineering, the University of Wisconsin, Madison, WI 53706, United States
[email protected] (T. Soysal), [email protected] (S. Kou)
Graphic Abstract The effectiveness of filler metals in reducing the susceptibility of Al alloys
2024 and 6061 to solidification cracking was evaluated using the Transverse Motion Weldability
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(TMW) test, in which the lower sheet in lap welding is moved at the speed V in the transverse
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direction of welding to cause cracking in the weld. The speed V at which one weld edge moves
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away from the other during crack propagation is close to that in actual welding, thus suggesting
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the test results are realistic. For welding 2024 Al, filler metal 2319 Al was least effective and
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filler metals 4043 Al and 4145 Al were both very effective, especially 4145 Al. For welding
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6061 Al, the new commercial filler metal 4349 Al designed to increase the weld strength was as effective as filler metal 4043 Al, which has been widely used for reducing solidification cracking
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in 6000-series Al alloys.
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Abstract The effectiveness of filler metals in reducing solidification cracking in welds of 2024 Al and 6061 Al was examined, these two Al alloys being highly susceptible to solidification cracking. The effectiveness was evaluated by the transverse motion weldability (TMW) test.
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2024 Al was welded with filler metals 2319 Al, 4043 Al and 4145 Al. 4043 Al and 4145 Al both reduced cracking effectively, but 4145 Al was significantly better. 6061 Al was welded with filler metals 4043 Al and 4943 Al (a new alloy designed to increase the weld strength of the 6000-series alloys), and the effectiveness was similar. Micrographs and curves of temperature T vs. fraction solid fS of the weld metals were used to help explain the test results.
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Keywords: Welding, solidification cracking, aluminum alloys, filler metals, weldability test.
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1. Introduction
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Welds of aluminum (Al) alloys are known to be susceptible to cracking during solidification.
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Because of solidification shrinkage (solid density > liquid density) and thermal contraction, the
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mushy zone (a weak semisolid between the weld pool and the solidified weld metal) must shrink.
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However, the mushy zone cannot shrink freely because it is connected to the much bigger and more rigid workpiece. Shrinkage can be more difficult if the workpiece is clamped down tightly.
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This obstructed shrinkage induces tensile deformation in the transverse direction of the mushy zone to cause cracking. To reduce the crack susceptibility, filler metals with nonmatching
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compositions are often required to adjust the composition of the weld metal in the fusion zone.
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Friction-stir welding can produce good-quality Al welds. However, arc welding can still be more versatile and cost effective in many applications if effective measures can be taken against the formation of defects in welds, especially cracking during solidification. Dudas and Collins (1966) studied the susceptibility of high strength wrought Al alloys to solidification cracking in welding with matching and non-matching filler metals. 2024 Al was 2
reported as the most crack-susceptible alloy in the 2000-series (Al-Cu) alloys, and 6061 Al the most crack-susceptible of all the Al alloys tested (Dudas and Collins, 1966). The filler metal 4043 Al significantly reduced crack susceptibility of 6061 Al, but no filler metal was reported to
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reduce the crack susceptibility of 2024 Al (Dudas and Collins, 1966). Many solidification cracking tests have been developed to evaluate the crack susceptibility of alloys. So far, the solidification cracking test most widely used in the welding industry and research has been the Varestraint test developed by Savage and Lundin (1965). The standard workpiece is 203 mm long by 102 mm wide by 12.7 mm thick. During welding, the workpiece of
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thickness H is suddenly bent in the welding direction against a mandrel (bending block) of
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predetermined radius R. A tensile strain of = H/(2R+H) × 100 % is induced at the top surface
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of the workpiece. The strain induces tension in the mushy zone to cause solidification cracking.
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The total or maximum crack length is used as the index for the susceptibility to solidification
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cracking. A transverse version of the Varestraint test, called transverse Varestraint, was
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subsequently developed by Senda et al. (1971, 1973), in which the workpiece is bent suddenly in the transverse direction of welding instead of longitudinal.
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Coniglio (2008) pointed out that the tensile strain in the Varestraint test is the global strain
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in the workpiece, instead of the local tensile strain in the mushy zone responsible for solidification cracking. He also pointed out that the strain rate caused by sudden bending is too
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fast as compared to that in welding practice. Another issue is associated with evaluating the effect of a filler metal on solidification cracking. The filler metal increases H by forming a crown on the workpiece surface. The crown height varies across the width of the weld, so does H and hence . This issue may be ignored if only a qualitative comparison of weldability is needed, without specifying the strain level of the weld. To avoid this issue, however, a two-step 3
procedure is needed, an example of which was described by Lippold et al. (1982). The first step is to make a bead-on-plate weld with a filler metal, and then remove the crown by milling to ensure a flat workpiece surface. The second step is to conduct the normal Varestraint test (gas-
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tungsten arc welding without a filler metal) by making a smaller weld within the fusion boundary of the first weld.
To help address these and other issues (such as the interference of solidification by liquation cracking) associated with Varestraint testing (Savage and Lundin, 1965; Senda et al., 1971, 1973), Soysal and Kou (2017, 2018) developed a simple test, called Transverse-Motion
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Weldability (TMW) test, in which lap welding is conducted while the lower sheet moves normal
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to the welding direction at a predetermined speed to induce transverse tension in the mushy zone
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and cause solidification cracking. As the lower sheet moves at the speed V, the weld edge on it
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also moves away at V from the stationary weld edge on the upper sheet. In the TMW test V can
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be as slow as that in actual gas-tungsten arc welding, in which one weld edge also moves away
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from the opposite weld edge spontaneously as shown by Matsuda et. al. (1980). The test can be conducted with or without a filler metal for welding. Filler metals were used and the test results
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(Soysal and Kou, 2017) were consistent with the filler metal guides (AlcoTec Wire Co.; Hobart Filler Met.). The test was also conducted without filler metals (Soysal and Kou, 2018). The crack
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susceptibility ranking was 6061 Al > 7075 Al > 2024 Al > 2219 Al, which agrees with the crack
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susceptibility ranking of commercial wrought Al alloys. Before the TMW test the Controlled Tensile Weldability (CTW) test was developed by
Coniglio et al. (2009). In the CTW test the workpiece is welded to a larger and thicker mounting plate, one on each lateral side. The plates were then mounted on a horizontal tensile testing machine to stretch the workpiece to induce tension in the transverse direction of the weld. Since 4
the mounting plates, workpiece, solidified weld metal and semisolid mushy zone are all being deformed during welding, an extensometer is mounted across the weld width on the bottom surface of the workpiece to measure the speed at which one weld edge moves away from the
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opposite weld edge, i.e., transverse deformation rate of the mushy zone. The test Soysal and Kou (2017, 2018) developed has some similarity to the CTW test, but the mounting plates, extensometer and tensile testing machine are not required.
The present study evaluated effectiveness of filler metals in reducing solidification cracking in two highly crack susceptible Al alloys, 2024 and 6061. The purpose was to provide
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experimental data that can be used for selecting filler metals to suppress solidification cracking
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in welding 2024 Al and 6061 Al.
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2. Experimental Procedure
The transverse-motion weldability (TMW) test used for assessing the solidification cracking
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susceptibility has been described in detail elsewhere (Soysal and Kou, 2017, 2018) and will not
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be repeated here. As shown in Fig. 1, during lap welding the upper sheet is stationary and the lower sheet moves at a predetermined speed V normal to the welding direction to induce tensile
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deformation in the mushy zone to cause cracking.
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Table 1 shows the actual compositions of the workpiece and filler metals (1.2 mm diameter)
used for welding. The upper sheet was 3.2 mm by 51 mm by 203 mm, and the lower sheet 3.2
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mm by 127 mm by 152 mm. The lower sheet was positioned to stick out of the upper sheet by 19 mm (0.75 in) before welding. A servomotor was preprogrammed by a computer to move the lower sheet. Apparently, by moving the lower sheet at a single constant speed throughout welding, the crack susceptibility can be evaluated based on crack initiation. However, in gas-
5
metal arc welding the filler metal tends to freeze faster and melt the workpiece less at the beginning of welding than during the steady state because the workpiece is initially cold. This can cause considerable scatter in the test results. Thus, it was decided to move the lower sheet
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faster initially to insure crack initiation and then slower for crack propagation. Consequently, in all experiments the moving speed of the lower sheet was 1.5 mm/s initially for a distance up to about 25 mm and then lowered to the predetermined level to investigate crack propagation. After the lower sheet started to move, the carriage was turned on to move the torch at the
Mushy-zone deformation rate = V
GMAW torch
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torn weld low er sh ee t
up (st p e r ati sh on ee ary t ) we dir ldin ec g tio n
low (m er s ov hee ing t )
arc pool
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screw
mushy zone moving at speed V
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predetermined travel speed, and the arc was initiated.
V
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crack
guide sheet
Cu base
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Fig. 1. Schematic sketch of test used for assessing susceptibility to solidification cracking (Soysal and Kou, 2017).
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The welding conditions for gas-metal arc welding (GMAW) were: 23 V welding voltage, 5.1
mm/s torch travel speed, 85 - 89 mm/s wire feed speed (welding current of 120 - 125 A), and
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3.54 x 10-4 m3/s Ar shielding. The torch was tilted 10o toward the joint and 10o backward (dragging). After welding, the fracture surfaces were examined by scanning electron microscopy (SEM). The transverse cross-sections of the welds were cut and mechanically polished. 6061 Al welds 6
were etched with Keller’s solution, consisting of 5 mL HNO3, 3 mL HCl, 2 mL HF and 190 mL distilled water. 2024 Al welds were etched with a solution consisting of 0.5 mL HF and 99.5 mL distilled water. The welds were then examined under optical and electron microscopy.
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3. Results Fig. 2 shows a 2024 Al workpiece after being welded with filler metal 2319 Al. The weld surface was cleaned with a stainless-steel wire brush before photographing. The initial moving speed of the lower sheet was 1.5 mm/s, resulting in the initial portion of the weld with a wider crack opening. After lowering the moving speed to 0.2 mm/s, the crack opening narrowed. The
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length of the narrower crack is labeled as Lcrack, and the length of the weld without the wider
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opening is labeled as Lweld. The ratio of Lcrack/Lweld is taken as the normalized length of crack
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propagation. The welds in the present study are shorter than those gas-metal arc welds in the
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previous study by the authors (Soysal and Kou, 2017). It was found that the results of shorter
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welds are more reproducible, i.e., with a narrower transition range from no crack to full crack. A
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longer weld tends to get wider as it approaches the end of the workpiece. The dendritic fracture surface shown by the SEM image in Fig. 3 confirms that the crack was caused by solidification
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cracking. The fracture surfaces of cracks that occur during solidification in welding and casting typically reveal dendrites (Matsuda et al.1978; Campbell, 2003). This is because such cracking
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occurs along grain boundaries near the end of solidification, along which thin liquid films are
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present. When cracking occurs, the thin liquid films quickly freezes over the dendrite arms, thus resulting in dendritic fracture surfaces. 3.1 Assessing filler-metal effectiveness Fig. 4 shows the welds made by welding 2024 Al with three different filler wires at the lowersheet moving speed of 0.4 mm/s. When filler wire 2319 Al is used, solidification cracking 7
propagates all the way through the weld. When the filler wire is switched to 4043 Al, solidification cracking is greatly reduced, propagating only slightly after the initiation period. With 4145 Al, the reduction is even better – no crack propagation at all. The results show clearly
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that filler metal 4043 Al or 4145 Al can be considered if solidification cracking occurs in welding 2024 Al.
In Fig. 5 the normalized crack length is plotted vs. the lower-sheet moving speed V for the 2024 Al welds made with the three filler wires. As shown in Fig. 5a, with filler metal 2319 Al the normalized crack length increases from 0 at V = 0.1 mm/s to 1.0 at 0.3 mm/s. The range of V
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over which the normalized crack length increases from 0 to 1.0 will be called the transition range
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A
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2319 Al under the welding conditions used.
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hereinafter. Thus, the transition range is 0.10 – 0.30 mm/s for 2024 Al welded with filler metal
Fig. 2. 2024 Al welded with filler metal 2319 Al: (a) overview, (b) enlarged. Lower sheet initially moved at 1.5 mm/s to ensure crack initiation and lowered to 0.2 mm/s for crack 8
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propagation. Lcrack and Lweld are, respectively, length of crack propagation and length of weld from beginning of crack propagation.
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A
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Fig. 3. Dendritic fracture surface of 2024 Al weld made with filler metal 2319 Al confirming solidification cracking.
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Fig. 4. 2024 Al welded with filler metals: (a) 2319 Al, (b) 4043 Al, and (c) 4145 Al and tested with the moving speed of 0.4 mm/s.
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Similar results are shown in Fig. 5b for 2024 Al welded with filler metal 4043 Al and in Fig.
5c for 2024 Al welded with filler metal 4145 Al. As shown, the transition range increases to 0.36 – 0.50 mm/s with filler metal 4043 Al. It increases further to 0.88 – 1.0 mm/s with filler metal 4145 Al.
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Fig. 6 shows the results of 6061 Al welded with two different filler metals. As shown in Fig. 6a, with filler metal 4943 Al the transition range is from 0.40 to 0.50 mm/s. With 4043 Al as the filler metal, the transition range is from about 0.38 to 0.50 mm/s as shown in Fig. 6b.
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Fig. 7 summarizes the results of the assessment of filler-metal effectiveness. A transition range at a higher V level suggests the lower sheet needs to be moved faster to cause cracking and hence a more effective filler metal for reducing cracking. As shown, filler metal 2319 Al is least effective for 2024 Al, and filler metal 4145 Al most effective. Filler metals 4943 Al and 4043 Al have similar effectiveness. Filler metal 4043 Al appears to reduce the crack susceptibility of
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D
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A
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2024 Al and 6061 Al to about the same level.
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2024 Al welded with three filler metals
1.0 0.9 0.8 0.7 0.6
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1.0
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Filler: 4145 Al
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full crack
0.2 0.4 0.6 0.8 Moving speed V, mm/s
transition range
0.2 0.4 0.6 0.8 Moving speed V, mm/s
full crack
0.5 0.4 0.3 0.2 0.1 0 0
transition range
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1.0 0.9 0.8 0.7 0.6
1.0
Filler: 4043 Al
no crack
0.5 0.4 0.3 0.2 0.1 0 0
SC RI PT
full crack
no crack
0.2 0.4 0.6 0.8 Moving speed V, mm/s
CC
Normalized crack length, Lcrack / Lweld
(c)
transition range
EP
Normalized crack length, Lcrack / Lweld
(b)
0.5 0.4 0.3 0.2 0.1 0 0
Filler: 2319 Al
no crack
Normalized crack length, Lcrack / Lweld
(a) 1.0 0.9 0.8 0.7 0.6
1.0
Fig. 5. Test results of 2024 Al welded with three filler metals: (a) 2319 Al; (b) 4043 Al; (c) 4145 Al.
11
6061 Al welded with two filler metals
SC RI PT
full crack 1.0
Filler: 4043 Al
U
transition range
0.2 0.4 0.6 0.8 Moving speed V, mm/s
N A 1.0
D
0.5 0.4 0.3 0.2 0.1 0 0
0.2 0.4 0.6 0.8 Moving speed V, mm/s
M
1.0 0.9 0.8 0.7 0.6
transition range
no crack
0.5 0.4 0.3 0.2 0.1 0 0
Filler: 4943 Al
full crack
Normalized crack length, Lcrack / Lweld
(b)
1.0 0.9 0.8 0.7 0.6
no crack
Normalized crack length, Lcrack / Lweld
(a)
TE
Fig. 6. Test results of 6061 Al welded with two filler metals: (a) 4943 Al; (b) 4043 Al. (b) 6061 Al welded with filler metals 4043 Al, 4943 Al 1.0 full 0.8 crack
0.6
full crack
Moving speed V, mm/s
0.8
transition range
1.0
EP
2024 Al welded with filler metals 2319 Al, 4043 Al, 4145 Al
CC
Moving speed V, mm/s
(a)
0.4
A
0.2 0
2319
no crack 4043
4145
increasing filler-metal effectiveness in reducing crack susceptibility (faster V required to cause cracking)
0.6 0.4 no crack
0.2 0
4043
4943
similar effectiveness
Fig. 7. Results of assessment of filler-metal effectiveness in welding: (a) 2024 Al (Fig. 5); (b) 6061 Al (Fig. 6). The faster the lower-sheet moving speed is required to stretch the mushy zone to cause cracking, the more effective the filler metal is in reducing the crack susceptibility.
12
3.2 Macrostructure and microstructure Fig. 8 shows the transverse cross-section of a 2024 Al weld made with filler metal 4145 Al. The areas of the upper and lower sheets in the weld represent the contribution of the base metal
SC RI PT
to the weld metal. The dilution level, i.e., the extent the filler metal is diluted by the base metal, is the ratio of the areas to the total area of the weld. It is about 50% for the 2024 Al welds and 47% for the 6061 Al welds. For each weld, the weld-metal composition can be calculated from the compositions of the workpiece and filler wire and the dilution level (Kou, 2003). The small rectangular box indicates the location where micrographs in Figs. 9 and 10 are shown in this and
U
the other welds, that is, the mid height of the fusion boundary in the upper sheet. Near the fusion
N
zone the heat-affected zone appears as a lighter-etching region due to solutionization of the
A
precipitates present in the original workpiece. Farther away from the fusion zone, it appears as a
EP
TE
D
M
darker-etching region of the precipitates that formed due to heating during welding (Kou, 2003).
A
CC
Fig. 8. Transverse cross-section of 2024 Al weld made with filler metal 4145 Al. Small rectangular box indicates location where micrographs were taken, i.e., fusion boundary at mid height of upper sheet. Solid lines indicate the fusion boundaries, and dotted lines the surfaces of the upper and lower sheets before welding. Fig. 9 shows the microstructure near the fusion boundaries of the 2024 Al welds made with
filler metals 2319 Al, 4043 Al and 4145 Al. The small boxes in Fig. 9b and c indicate the locations where the SEM images in Fig. 11 were taken. Dendritic columnar grains can be seen in the weld metal. The eutectic exists in the interdendritic areas. With much Si provided by fillers 13
4043 Al and 4145 Al, the eutectic becomes darker etching than without Si. Fig. 10 shows the microstructure near their fusion boundaries of the 6061 Al welds made with filler metals 4943 Al and 4043 Al. The eutectic appears very thin but still continuous. Fig. 11 shows the SEM images
SC RI PT
of the eutectics in 2024 Al welds made with filler metals 4043 Al and 4145 Al. The results of
A
CC
EP
TE
D
M
A
N
U
EDX composition measurements are given in Table 2. As shown, these eutectics are Si rich.
Fig. 9. Optical micrographs near fusion boundaries (dotted lines) of 2024 Al welded with fillers: (a) 2319 Al; (b) 4043 Al; (c) 4145 Al. Rectangular boxes in (b) and (c) indicate the locations where SEM images in Fig. 11 were taken. 14
SC RI PT U N A
M
Fig. 10. Optical micrographs near fusion boundaries (dotted lines) of 6061 Al welded with fillers: (a) 4943 Al; (b) 4043 Al. Very thin but still continuous eutectic (dark etching) suggests thin continuous liquid films near end of solidification.
D
3.3 T-fS Curves for 2024 Al welds made with filler metals 4043 and 4145 Al
TE
As mentioned previously, the level of filler-metal dilution by the base metal can be
EP
determined from the transverse macrograph of the weld. The dilution level can in turn be used to calculate the weld-metal composition (Kou, 2003) as follows: (wt% of element E in weld metal)
CC
= (wt% of element E in base metal) × (dilution) + (wt% of element E in filler metal) × (1 − dilution). Table 3 shows the compositions of the 2024 Al welds made with filler metals 4043 and
A
4145 Al. Based on these compositions, the commercial thermodynamic software Pandat (2018), the aluminum database PanAluminum (2018) and the Scheil solidification model were used to calculate the curves of T (temperature) vs. fS (fraction solid) of these welds. These curves, i.e., the solidification paths, of the welds are shown in Fig. 12. The points at which solid phases begin
15
to form during solidification are indicated. As can be seen on both curves, the FCC phase (the Al-rich phase) starts to form first and other phases follow. The diamond phase is essentially pure Si with the trace amount of Al in it. Fig. 12a shows Al3Ti precipitates from the liquid (at 669 oC)
SC RI PT
before the FCC phase starts to form. As shown in Table 1, filler metal 4043 Al contained 0.2 wt%
EP
TE
D
M
A
N
U
Ti.
CC
Fig. 11. SEM images of eutectics in 2024 Al welded with fillers: (a) 4043 Al (inside boxed area in Fig. 9b); (b) 4145 Al (inside boxed area in Fig. 9c). The compositions measured by EDX at the locations indicated by the circles are given in Table 2.
A
The phases shown along the T-fs curves in Fig. 12 can be compared with the results of EDX
measurements in Table 2 to help identify the phases shown in Fig. 11. For 2024 Al welded with filler metal 4043 Al (Fig. 11a), in view of the Si and Al contents, Point 1 in Fig. 11a seems to correspond to the combination of the FCC phase and the diamond phase. Likewise, in view of
16
the Si, Cu and Al contents, Point 2 seems to correspond to FCC + diamond + AlCu_Ө. As for 2024 Al welded with filler metal 4145 Al (Fig. 11b), Point 1 seems to correspond to FCC + diamond phases. Point 2 is likely to correspond to the combination of FCC + diamond +
SC RI PT
β_AlFeSi + Al15_FeMn3Si2 + AlCu_Ө.
Solidification paths of 2024 Al welds 650
Al3Ti
made with filler 4043 Al
Al15_FeMn3Si2
Fcc
β_AlFeSi
600
Diamond (Si) 550 AlCu_Ө 0.2
0.4 0.6 fraction solid fs
650
made with filler 4145 Al Fcc
Al15_FeMn3Si2
600
D
Diamond (Si) β_AlFeSi
550
Q_Al5Cu2Mg8Si6 0
0.2
AlCu_Ө
0.4 0.6 fraction solid fs
1
0.8
EP
500
TE
Temperature T, ºC
(b)
1
0.8
N
0
A
500
U
Al8FeMg3Si6+Q_Al5Cu2Mg8Si6
M
Temperature T, ºC
(a)
CC
Fig. 12. Solidification paths calculated using Pandat and PanAluminum for 2024 Al welds made with fillers: (a) 4043 Al; (b) 4145 Al. Discussion
4.1
Crack initiation and propagation
A
4.
As mentioned previously, at the beginning of GMAW filler-metal droplets tend to freeze
faster and hence less able to melt the base metal because the workpiece is still cold. This can cause scatter in the results of crack-susceptibility testing based on crack initiation, i.e., moving the lower sheet at a constant speed V throughout welding. To avoid this problem, crack 17
susceptibility testing was conducted based on crack propagation, i.e., moving the lower sheet faster initially to ensure crack initiation but slower subsequently for crack propagation. Crack susceptibility testing based on crack propagation instead of crack initiation can be
SC RI PT
justified as follows. Kou (2015) proposed a criterion for cracking during solidification by considering the space between two columnar dendritic grains near their roots. He showed that for a weld metal with a higher maximum │dT/d(fS)1/2│ (T: temperature; fS: fraction of solid), the space decrease caused by its slower grain growth and liquid feeding is more likely to be slower than the space increase caused by the tensile deformation separating the grains (Kou, 2015).
U
Thus, it is more likely for a void (i.e., crack) to form inside the space either by nucleation (crack
N
initiation) or by extension of an existing crack into it (crack propagation). Consequently, a weld
A
metal with a higher maximum │dT/d(fS)1/2│ can rank higher in the crack susceptibility in the
M
present test either based on crack initiation or crack propagation. Oxides or micro porosity can
D
serve as the sites for nucleation of cracks (Campbell 2003; Coniglio, Cross, 2009), so can the
TE
free surface of the mushy zone (Campbell, 2014). In lap welding such as the present test, the free surface includes the surface of the mushy zone at the top and that on the side at the gap between
EP
the upper and lower sheets. Soysal and Kou (2017, 2018) demonstrated that the cracksusceptibility ranking of commercial wrought Al alloys using the present test based on crack
CC
propagation agrees with the ranking predicted based on the maximum│dT/d(fS)1/2│as the crack
A
susceptibility index. Furthermore, it also agrees with the ranking reported by Dowd (1952) and Dudas and Collins (1966) using other crack-susceptibility tests. The crack susceptibility of the welds in the present study was also predicted based on the maximum│dT/d(fS)1/2│and the weldmetal compositions, and it agreed well with the test results (Soysal and Kou, 2018b).
18
Kou’s criterion for solidification cracking and index for the crack susceptibility (Kou, 2015) can be related to the TMW test. In the TMW test the motion of lower sheet during lap welding
SC RI PT
can cause the columnar grains near the centerline of the mushy zone to separate from each other. For an alloy with a high │dT/d(fS)1/2│near (fS)1/2=1, the grains grow thicker slowly near their roots as they grow longer to form a long liquid channel between them to resist liquid feeding, thus delaying the bonding between the grains and slowing down liquid feeding through the channel. Consequently, even a slow speed of the lower sheet can separate the grains to cause
U
cracking before bonding or liquid feeding can occur to resist cracking. The slower the speed is,
Effectiveness of filler metals
A
4.2
N
the higher the crack susceptibility.
M
Al filler metal guides (AlcoTec Wire Co.; Hobart Filler Met.) provide useful information for
D
designing the welds for various purposes or applications of Al welds, such as better resistance to
TE
solidification cracking, higher strength, better resistance to corrosion etc. However, they do not include 2024 Al. Fig. 7a can be a guide for selecting filler metals to minimize the chance for
EP
solidification cracking to occur in welding 2024 Al.
CC
By keeping the welding parameters the same in making welds with different filler metals, the effect of the filler metal on solidification cracking can be evaluated. When the filler metal is
A
changed, the composition, solidification path and hence crack susceptibility of the weld metal are changed significantly. The weld width may also be changed, but usually not much. Ideally, the welding parameters can be changed slightly to keep the weld width identical, but this is very difficult to do, and the effect may be small. The welding parameters can affect solidification cracking, but the effect of the weld-metal composition dominates (Kou, 2003). This is why an 19
alloy that has a high tendency to crack in casting also has a high tendency to crack in welding. If changing the welding parameters increases the dilution, the effectiveness of the filler metal in reducing cracking can be expected to decrease. In MIG welding, increasing the welding current
SC RI PT
(the wire feeding speed) causes more base metal to melt but more filler metal also melts. So, the dilution may not change a lot. Decreasing the travel speed can have a similar effect on dilution. Fig. 7a shows the transition range above which the lower sheet needs to be moved to cause full cracking in welds of 2024 Al and hence the effectiveness of the filler metal in reducing their solidification cracking are affected significantly by the filler metal used. 4145 Al is most
N
U
effective and 2319 Al least.
A
The filler metal guide (Hobart Filler Met.) indicates the new filler metal 4943 Al is effective
M
for reducing solidification cracking in 6000 series Al alloys, without referring to the dilution level or any reports of crack susceptibility testing. As can be seen in Table 1, 4943 Al is close to
D
4043 Al in composition, but the Mg/Si ratio is raised significantly to 0.074 in 4943 Al from
TE
0.010 in 4043 Al to increase the weld-metal strength. According to the developer of 4943 Al, the weld made with 4943 Al is higher in strength than that made with 4043 Al in the as-welded
EP
condition and is heat-treatable to gain extra strength by postweld artificial aging (Maxal).
CC
However, it is unclear how this much higher Mg/Si ratio may affect solidification cracking. The test results shown in Fig. 7b indicate that the effectiveness of 4943 Al in reducing solidification
A
cracking in welding 6061 Al is similar to that of 4043 Al, at least under the experimental condition used in the present study. Fig. 9 shows a dark-etching phase appears in the fusion-zone microstructure of 2024 Al (~Al-4.6Cu) when the filler metal is changed from 2319 Al (~Al-6.3Cu) to 4043 Al (~Al-5Si).
20
The calculated solidification paths of the 2024 Al welds made with filler metal 4043 Al and 4145 Al are shown in Fig. 12. With filler 4043 Al, the Si-rich phase (diamond A4 in structure) starts to form at about fS = 0.8 (about T = 550°C). With filler metal 4145 Al, the Si-rich phase starts to
SC RI PT
form significantly earlier at about fS = 0.6 (about T = 555°C). In both cases, the increase in the fraction solid with cooling is faster after (than before) the Si-rich phase starts to form. With 4145 Al, the fraction solid increases rapidly with decreasing temperature, causing the Al-rich dendrites to quickly bond together to resist solidification cracking (Kou 2015), (Liu and Kou, 2015, 2016, 2017), (Liu, Duarte and Kou, 2017). Although 4145 Al best resists solidification cracking in
U
2024 Al, other weld properties need to be considered as well, e.g., toughness and corrosion
Strain rate in mushy zone
A
4.3
N
resistance, depending on the application of the resultant weld.
M
In gas-tungsten arc welding of Al alloys, Matsuda et. al. (1980) measured the speed at which
D
one weld edge moved away from the opposite weld edge, and it was in the range of 0-0.9 mm/s,
TE
close to that in Figs. 5 and 6. Thus, in the TMW test the speed V of the weld edge on the lower sheet relative to that on the upper sheet is realistic from the practical welding point of view, and
EP
the strain rate experienced by the mushy zone can be expected to represent that in actual welding.
CC
Although the average strain rate of the mushy zone in the transverse direction can be taken as V divided by the weld width W, the local strain rate near the crack is likely significantly higher than
A
V/W. Bakir et al. (2018) measured the local strain rate near the crack in laser-beam welding of a stainless steel during the CTW test. At the crosshead speed of 1.2 to 2.3 mm/s of the tensile testing machine, the global strain rate of the entire mushy zone was 4 to 8 %/s and the local strain rate near the crack was 18 to 29 %/s.
21
It might be possible to estimate the local strain rate near the crack in the TMW test. The transverse micrographs of the TMW tested welds showed no evidence of separation of dendrites from each other except near the crack (Soysal and Kou, 2018). In the areas next to both sides of
SC RI PT
the main crack, intergranular micro fissures were found, more or less parallel to the crack and often filled with dark-etching eutectic (not shown). Closer to the crack, the micro fissures were wider. Thus, as an approximation, tensile deformation can be assumed to occur mostly in the areas next to both sides of the main crack. Preliminary examination of transverse micrographs near cracks in some welds showed the total width of these areas was on the order of 1 to 2 mm.
U
This suggests that, just before cracking occurred, the width of the area deformed by tensile
N
deformation, D, was about 1.5 mm. The width of the weld and hence the mushy zone W was on
A
the order of 10 mm. Thus, the local average strain rate V/D was significantly higher than the
M
overall average strain rate V/W. If 2024 Al welded with filler metal 4043 Al is taken as an example just for the purpose of discussion, the minimum V needed to cause cracking is about 0.4
D
mm/s according to Fig. 5b. The corresponding minimum overall average strain rate is V/W =
TE
0.04/s (0.4 mm/s ÷ 10 mm) or 4%/s. Likewise, the corresponding minimum local average strain
EP
rate is V/D = 0.27/s (0.4 mm/s ÷ 1.5 mm) or 27%/s. Further analysis of the local average strain rate is needed but not here as the focus of the present study is on the effectiveness of filler metals
CC
in reducing the crack susceptibility.
A
4. Conclusions
The effect of the commercial Al filler metals on reducing the solidification-cracking
susceptibility of two highly crack susceptible Al alloys 2024 and 6061 was investigated using the TMW test. The following conclusions can be drawn from the test results:
22
1. For welding 2024 Al, filler metal 4145 Al is highly effective against solidification cracking, 4043 Al less effective, and 2319 Al least effective. Thus, in situations where solidification cracking in 2024 Al welds is a major concern, 4043 Al or 4145 Al can be
SC RI PT
considered as the filler metal. 2. The calculated solidification paths of the 2024 Al welds show that the Si-rich phase tends to form at about 550 – 555oC during solidification but significantly earlier with filler metal 4145 Al than 4043 Al. With 4145 Al, after the formation of the Si-rich phase, the fraction solid increases rapidly during cooling to bond the Al-rich dendrites to resist
U
cracking.
N
3. For welding 6061 Al, the new filler metal 4943 Al is as effective against solidification
A
cracking as the traditional filler metal 4043 Al. Thus, if a high weld-metal strength is a
M
high priority, filler-metal 4943 Al can be considered.
D
5. Acknowledgements
TE
This work was supported by the National Science Foundation under Grant No. DMR 1500367. The graduate student Tayfun Soysal was funded by the Ministry of National Education of
EP
Republic of Turkey during the project.
CC
6. References
AlcoTec Wire Corporation, 2015. www.alcotec.com/us/en/support/upload/ALC-
A
10030C_AlcoTec_Alloy_Selection_Brochure_Tabloid.pdf.
Bakir, N., Gumenyuk, A., Rethmeier, M., 2018. Investigation of solidification cracking susceptibility during laser beam welding using an in-situ observation technique, Sci. Tech. Weld. Join., 23(3), 234–240.
23
Campbell J., Castings, 2nd edition, Butterworth Heinemann, Oxford, UK, 2003; pp. 216-247. Campbell, J., Private Communications, United Kingdom, June 2014. Coniglio, N., 2008. Aluminum alloy weldability: Identification of weld solidification cracking
SC RI PT
mechanisms through novel experimental technique and model development. Doctoral thesis, Otto-von-Guericke University, Magdeburg, Berlin.
Coniglio, N., Cross, C.E., 2009. Mechanisms for solidification crack initiation and growth in aluminum welding. Metal. Mater. Trans. A, 40A (11), 2718–2728.
U
Cross, C. E., 2015. On the Origin of Weld Solidification Cracking, Hot Cracking Phenomena in
N
Welds, 3-18.
A
Dowd, J. D. 1952. Weld cracking of aluminum alloys. Weld. J., 31, 448s-456s.
M
Dudas, J. H., and Collins, F. R. 1966. Preventing weld cracks in high strength aluminum alloys.
TE
Hobart Filler Metals, 2018.
D
Weld. J., 45, 241s-249s.
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http://www.hobartbrothers.com/downloads/aluminum_selecti_1lOo.pdf Kou, S., 2015. A criterion for cracking during solidification. Acta Mater., 88, 366-374.
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Kou, S., Welding Metallurgy, 2nd edition, J. Wiley and Sons, Hoboken, NJ, 2003; pp. 103-114,
A
149-151.
Liu, J., Kou S., 2015. Effect of diffusion on susceptibility to cracking during solidification, Acta Mater., 100, 359-368.
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Liu, J., Kou S., 2016. Crack susceptibility of binary aluminum alloys during solidification, Acta Mater., 110, 84-94. Liu, J., Kou, S., 2017. Susceptibility of ternary aluminum alloys to cracking during solidification,
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Acta Mater., 125, 513-523. Liu, J., Duarte H.P., Kou S., 2017. Evidence of back diffusion reducing cracking during solidification, Acta Mater., 122, 47-59.
Matsuda, F., Nakata, K., Harada, S., 1980. Moving characteristics of weld edges during
U
solidification in relation to solidification cracking in GTA weld of aluminum alloy thin sheet
N
(Weld. Mech., Strength & Design). Trans. JWRI, 9(2), 225-235.
A
Matsuda, F., Nakagawa, H., Ogata, S., Katayma, S., 1978. Fractographic Investigation on
M
Solidification Crack in the Varestraint Test of Fully Austenitic Stainless Steel-Studies of
D
Fractography of Welded Zone (III). Trans. JWRI, 7(1), 59-70.
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Maxal, 2008. Maxal 4943. Maxal, Traverse City, MI, may be accessible at www.maxal.com/4943_datasheet.pdf,
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PanAluminium, 2018. Thermodynamic database for commercial aluminum alloys, Computherm
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LLC, Madison, WI 53719, 2018. Pandat, 2018. Phase diagram calculation software package for multicomponent systems,
A
Computherm LLC, Madison, WI 53719, 2018.
Savage, W.F., Lundin, C.D., 1965. The Varestraint test, Weld. J. 44, 433s-442s.
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Senda, T., Matsuda, F., Takano, G., 1973. Solidification crack susceptibility for weld metals with the Trans-Varestraint test. Part 2: Commercially Used Aluminum and Aluminum Alloys. Yosetsu Gakkai- Shi. 42(1), 48-56.
SC RI PT
Senda, T., Matsuda, F., Takano, G., Watanabe, K., Kobayashi, T., Matsuzaka, T., 1971. Fundamental investigations on solidification crack susceptibility for weld metals with TransVarestraint test. Trans. Japan Weld. Soc., 2(2), 141-162.
Soysal, T., Kou, S., 2017. A simple test for solidification cracking susceptibility and filler metal
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effect. Weld. J., 96(10), 389s-401s.
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Soysal, T., Kou, S., 2018a. A simple test for assessing solidification cracking susceptibility and
A
checking validity of susceptibility prediction. Acta Mater., 143, 181-197.
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Soysal, T., Kou, S., 2018b. Prediction of Filler-Metal Effect on Solidification Cracking in 2024
A
CC
EP
TE
D
Al and 6061 Al, Sci. Tech. Weld. and Join., in preparation.
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Si
Fe
Cu
Mn
Mg
Cr
Ti
Zr
Zn
Al
0.01 0.01
0.01 -
-
Bal. Bal.
-
0.18 -
0.10 0.04 -
Bal. Bal. Bal. Bal.
SC RI PT
Sheets 2024 0.08 0.16 4.6 0.61 1.3 0.01 0.02 6061 0.666 0.387 0.245 0.099 1.083 0.1 0.025 Wires 2319 0.1 0.15 6.3 0.3 0.15 4043 5.2 0.8 0.3 0.05 0.05 0.001 0.20 4145 9.9 0.2 3.9 0.01 0.05 0.01 4943 5.42 0.12 0.005 0.005 0.4 0.001 0.017 Table 1. Actual compositions of materials in weight percent.
V
Si Fe Cu Mn Mg Al wt%; at% wt%; at% wt%; at% wt%; at% wt%; at% wt%; at% 2024-4043 Pt 1 13.6; 13.1 86.4; 86.9 2024-4043 Pt 2 9.7; 10.9 23.7; 11.7 66.6; 77.4 2024-4145 Pt 1 36.5; 35.5 0.6; 0.7 62.9; 63.8 2024-4145 Pt 2 12.5; 15.3 6.6; 4.1 27; 14.7 4.6; 2.9 49.3; 63.0 Table 2. Compositions (in weight % and atomic %) measured by EDX in 2024 Al welds made with filler metals 4043 and 4145 Al.
M
A
N
U
Base-Filler #
A
CC
EP
TE
D
Si Fe Cu Mn Mg Cr Ti V Zr Zn Al sheet-filler dilution 2024-4043 48.7 % 2.71 0.49 2.39 0.32 0.66 0.01 0.11 0.00 0.00 0.05 Bal 2024-4145 50.7 % 4.92 0.18 4.25 0.31 0.68 0.01 0.01 0.01 0.01 002 Bal Table 3. Compositions (in weight %) of 2024 Al welds made with filler metals 4043 and 4145 Al.
27